This invention relates to a lead-free metallic body solder and, more particularly, to a tin-base body solder containing copper and zinc.
Body solder is traditionally a metal alloy adapted for application to a fabricated steel or other metal surface to fill depressions therein and thereby form a smooth decorative surface. For example, in the automotive industry and elsewhere, body solder is used to fill a depression designed about a welded seam or to repair a dent. Heretofore, a lead-base alloy containing tin or antimony was used as a body solder because it was capable of being conveniently applied. When moderately heated, the alloy partially melts to form a workable paste that is readily spreadable onto a steel surface using an oiled wooden paddle and hand applied pressure. The workable paste is formed over a wide temperature range, which substantially enhances its spreadability. After being applied and upon cooling, the alloy forms a dense, tightly adherent fill having a surface adapted for finishing by grinding and printing in conjunction with the surrounding steel surface. Although the lead-base alloy is generally adequate as a body solder, the use of lead requires careful handling in the plant environment and is being reduced.
Therefore, it is an object of this invention to provide a metallic body solder requiring no lead content, which solder is adapted to be heated and applied as a workable paste to suitably fill depressions in a fabricated steel surface in a manner similar to traditional lead-base body solders. The body solder exhibits good adhesion, good grindability and good paintability, comparable to the lead-base solders.
It is a more particular object of this invention to provide a body solder alloy composed predominantly of tin and containing copper and zinc, but no appreciable lead. The alloy forms a spreadable thixotropic paste when heated to within a broad range of moderately elevated temperatures. The paste is suitable for spreading onto a steel surface without heat damage and, upon cooling, bonds thereto. In addition, the solder is capable of providing a paintable surface that resists sagging or flowing at typical curing temperatures.
It is also an object of this invention to provide a method of filling depressions in a fabricated steel surface prior to painting, which method includes heating a tin-base copper-zinc alloy to within a broad range of moderately elevated temperatures to form a spreadable paste. The paste is suitably applied to the depression without heat damage to the steel and, upon cooling, bonds thereto. The filled surface is suitable for painting, in accordance with conventional steel surface painting practices, and remains intact during paint curing.